3,382 research outputs found
Constraining a fourth generation of quarks: non-perturbative Higgs boson mass bounds
We present a non-perturbative determination of the upper and lower Higgs
boson mass bounds with a heavy fourth generation of quarks from numerical
lattice computations in a chirally symmetric Higgs-Yukawa model. We find that
the upper bound only moderately rises with the quark mass while the lower bound
increases significantly, providing additional constraints on the existence of a
straight-forward fourth quark generation. We examine the stability of the lower
bound under the addition of a higher dimensional operator to the scalar field
potential using perturbation theory, demonstrating that it is not significantly
altered for small values of the coupling of this operator. For a Higgs boson
mass of we find that the maximum value of the fourth
generation quark mass is , which is already in conflict
with bounds from direct searches.Comment: 6 pages, 2 figure
Estimating Abundance from Counts in Large Data Sets of Irregularly-Spaced Plots using Spatial Basis Functions
Monitoring plant and animal populations is an important goal for both
academic research and management of natural resources. Successful management of
populations often depends on obtaining estimates of their mean or total over a
region. The basic problem considered in this paper is the estimation of a total
from a sample of plots containing count data, but the plot placements are
spatially irregular and non randomized. Our application had counts from
thousands of irregularly-spaced aerial photo images. We used change-of-support
methods to model counts in images as a realization of an inhomogeneous Poisson
process that used spatial basis functions to model the spatial intensity
surface. The method was very fast and took only a few seconds for thousands of
images. The fitted intensity surface was integrated to provide an estimate from
all unsampled areas, which is added to the observed counts. The proposed method
also provides a finite area correction factor to variance estimation. The
intensity surface from an inhomogeneous Poisson process tends to be too smooth
for locally clustered points, typical of animal distributions, so we introduce
several new overdispersion estimators due to poor performance of the classic
one. We used simulated data to examine estimation bias and to investigate
several variance estimators with overdispersion. A real example is given of
harbor seal counts from aerial surveys in an Alaskan glacial fjord.Comment: 37 pages, 7 figures, 4 tables, keywords: sampling, change-of-support,
spatial point processes, intensity function, random effects, Poisson process,
overdispersio
The impact of environmental variability on Atlantic mackerel Scomber scombrus larval abundance to the west of the British Isles
The value of the Continuous Plankton Recorder (CPR) fish larvae dataset, with its extensive spatio-temporal coverage, has been recently demonstrated with studies on long-term changes over decadal scales in the abundance and distribution of fish larvae in relation to physical and biological factors in the North Sea. We used a similar approach in the west and southwest area of the UK shelf and applied a principal component analysis (PCA) using 7 biotic and abiotic parameters, combined with Hierarchical Cluster Analysis (HCA), to investigate the impact of environmental changes in the west and southwest area of the UK shelf on mackerel larvae during the period 1960–2004. The analysis revealed 3 main periods of time (1960–1968; 1969–1994; 1995–2004) reflecting 3 different ecosystem states. The results suggest a transition from an ecosystem characterized by low temperature, high salinity, high abundances of zooplankton and the larger phytoplankton groups, to a system characterized by higher temperature, lower salinities, lower abundances of zooplankton and larger phytoplankton and higher abundances of the small phytoplankton species. Analysis revealed a very weak positive correlation between the Second principal component and mackerel larvae yearly abundance, attributed to the North Atlantic Oscillation (NAO). The results presented here are in broad accord with recent investigations that link climatic variability and dynamics of mackerel reproduction. However, the growing body of literature that documents statistical correlations between environment and mackerel needs to be supplemented by local process studies, to gain more insight and to be able to predict mackerel response to climate change scenarios. Utilising the strength of the CPR dataset, namely its unique temporal coverage, in an analysis where other data (such as egg surveys) are drawn in to compensate for the spatial issues could prove to be the way forward
Higgs boson mass bounds in the presence of a heavy fourth quark family
We present Higgs boson mass bounds in a lattice regularization allowing thus
for non-perturbative investigations. In particular, we employ a lattice
modified chiral invariant Higgs-Yukawa model using the overlap operator. We
show results for the upper and lower Higgs boson mass bounds in the presence of
a heavy mass-degenerate quark doublet with masses ranging up to 700 GeV. We
perform infinite volume extrapolations in most cases, and examine several
values of the lattice cutoff. Furthermore, we argue that the lower Higgs boson
mass bound is stable with respect to the addition of higher dimensional
operators to the scalar field potential. Our results have severe consequences
for the phenomenology of a fourth generation of quarks if a light Higgs boson
is discovered at the LHC
Handover parameter optimization in LTE self-organizing networks
This paper presents a self-optimizing algorithm that tunes the handover (HO) parameters of a LTE (Long-Term Evolution) base station in order to improve the overall network performance and diminish negative effects (call dropping, HO failures). The proposed algorithm picks the best hysteresis and time-to-trigger combination for the current network status. We examined the effects of this self-optimizing algorithm in a realistic scenario setting and the results show an improvement from the static value settings
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